This invention relates to a damper device for a motor used, for example, in a power window of an automobile.
Recently, with an increasing tendency for people to wish high-class cars (particularly, passenger cars), an increased percentage of cars have now been equipped with power windows, and therefore an increased number of motors have been used. When a switch of the power window is kept turned on, a window glass pane moves upward or downward, and when it comes into contact with a window frame, the motor is forcibly stopped. At this time, the motor as well as a speed reducer is subjected to an impact and therefore a damper or buffer device is incorporated so as to dampen such an impact to thereby prevent the breakage of the speed reducer.
A conventional motor damper device includes a worm wheel of a synthetic resin, a torque transmission plate or disk of stainless steel, and a damper/coupling member of rubber interposed between the worm wheel and the torque transmission disk, through which the worm wheel is coupled to the torque transmission disk. The worm wheel is operatively connected to the motor. The torque transmission disk is operatively connected to an output shaft for moving a window glass pane upward or downward.
When the window glass pane comes into contact with the window frame, the rotation of the output shaft is forcibly stopped, but at this moment the motor is still rotating, and therefore an impact force develops in the device.
At this time, the damper/coupling member is elastically deformed or twisted to absorb the impact, thereby preventing the tooth of the worm wheel from breakage.
With the above conventional construction, however, when a large load due to some external factor is applied to the window glass pane, a large twisting force is exerted on the damper/coupling member, so that the engagement between the torque transmission disk and the damper/coupling member and the engagement between the worm wheel and the damper/coupling member are released. Therefore the worm wheel idles, which results in a failure to open and close the window glass pane. There is also a drawback that the locking becomes ineffective, so that the window glass pane can be manually opened from the exterior.